How to use conditional edge with N-to-N node connections?

[Haoyuan-L]

Hi all, I have a question regarding the conditional edge in Langgraph.

I know in langgraph we can provide a dictionary to map the next node in the conditional edge:
graph.add_conditional_edges("node_a", routing_function, {True: "node_b", False: "node_c"})

I also realize that Langgraph supports N-to-1 node in this way:
builder.add_edge(["node_a", "node_b", "node_c"], "aggregate_node")
(The reason I must wrap all upstream nodes inside a list is to ensure that I receive all the nodes' state before entering the next node.)

Now, in my own circumstance, I have N-to-N node connections, where I have N upstream nodes, and each upstream node can navigate to a universal aggregated node or a node-specific (not shared across each upstream node) downstream node.

Could anyone explain how to construct this conditional edge in Langgraph? Thank you in advance.